What is this feeling?

Felt this feeling about a year ago but it has come back up. I've now noticed it is triggered by any thought of my partner leaving me (breaking up with me or dying, all of that). It is a painful sickness feeling in the gut. I like being alone it never bothers me to be myself in a room but I feel a wash of fear and realisation of how small and alone I am in the room. The sickness feeling leaves me unable to really walk and or live as it makes me want to jump off the nearest bridge.

Does anyone know what this feeling is? I have a feeling it is due to past trauma but who knows.